Selma Dritz is a name that could have been ripped from the pages of a hardboiled detective novel by Dashiell Hammett. But hers was a true story reflecting the noir grit of a more recent time: the early days of the AIDS epidemic in San Francisco.

Selma Dritz was in her 50s when she joined the San Francisco Department of Public Health in 1968 as an infectious disease epidemiologist. Her introduction to the city’s gay community, then one of the largest and most open in the world, began with an explosion of amoebic dysentery.

Rates of the parasitic infection had grown to 50 times those of the city as a whole, spread by oral-anal contact known as “rimming.” Her education in the sexual mores of the community was eye opening. She combined that knowledge with non-judgmental professionalism to pioneer educational efforts and pleas for safer sexual practices.

“Pneumocystis Pneumonia—Los Angeles.” This innocuously sounding paper announced the birth of HIV/AIDS on 5 June 1981 in Morbidity and …

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